This invention relates generally to radio-frequency (rf) mixers, and more particularly, to rf mixers for use in processing millimeter-wave signals, i.e. signals having a wavelength of the order of a millimeter. A mixer is a device used in communications equipment, and particularly in radio receivers, to convert an rf signal to an intermediate-frequency signal of lower frequency. The mixer heterodynes, or mixes, the rf signal with a different locally generated rf signal, referred to as the local oscillator (LO) signal. The mixer generates signal components both at the sum of the two input frequencies and at the difference of the input frequencies. By means of an appropriate low-pass filter, the difference signal is obtained as the output signal.
For millimeter-wave signals, rf waveguides have been traditionally used to transmit the rf input signals to mixers. Waveguides are basically hollow conductive tubes, usually of rectangular cross section. They transmit and confine electromagnetic energy with relatively low losses, but they are relatively bulky, and correspondingly costly. As communication activities in the millimeter-wave band have increased, there has developed a need in many receiver and communication system applications for a light-weight, low-cost local-oscillator/mixer assembly. Ideally, the assembly should also have good frequency stability, even in varying temperature conditions. In the past, frequency stability has been obtained by means of bulky and expensive phase-locked loop circuits. Other important requirements for a local-oscillator/mixer assembly are a low mixer conversion loss, and a capability of operation over a relatively wide frequency band of rf signals. The present invention meets these requirements and has other advantages that will become apparent from the following summary of the inventive aspects.